1. Field of the Invention
The present invention relates to a construction of an electromagnetic drive for controlling the amount of light of a luminous flux.
2. Description of the Related Art
Hitherto, an electromagnetic unit, which is an electromagnetic drive, is employed in a light amount controlling unit such as a light exposure controlling unit for controlling the light exposure of a camera or the like as a driving source. For example, a light amount controlling unit for a conventional lens barrel shown in a cross section in FIG. 19 employs an electromagnetic unit shown in a cross section in FIG. 20 as a drive source.
The conventional lens barrel 110 includes a taking lens 112 held by a lens frame 111, and an opening 111a is provided on the lens frame 111 at the position behind the taking lens. Two shutter blades 113, 114 are rotatably supported by supporting pins 117b, 117a around the opening 111a. The shutter blades 113, 114 are rotated by the electromagnetic unit 100 via a drive pin 115a of a shutter lever 115 to open and close the opening 111a. 
The electromagnet unit 100 is a plunger type electromagnet unit, and comprises a solenoid including a yoke 103, a ferromagnetic member 104, and a bobbin 102 supported by the yoke 103 and having a coil 101 wound thereon, and a plunger 105 being a movable iron core to be inserted into a hollow space portion of the bobbin 102, as shown in a cross sectional view of FIG. 20. The plunger 105 is urged by a coil spring 106 toward the direction of projection, and is sucked when the coil 101 is energized by a power source 107.
An end of the shutter lever 115 rotatably supported by the lens frame 111 abuts against the distal end of the plunger 105. When the coil is not energized, the plunger 105 is projected and the shutter blades 113, 114 are rotated to the close position by the shutter lever 115. When the coil is energized, the plunger 105 is sucked and thus the shutter lever 115 rotates clockwise by a torque of a torsion spring 116, and the shutter blades 113, 114 are rotated into the open position.
The light exposure controlling unit disclosed in Japanese Unexamined Patent Application Publication No. 4-194912 also employs a plunger-type electromagnetic drive having the same construction as the electromagnet unit 100 applied to the conventional light exposure controlling unit (light amount controlling unit) described above as a driving source.
In the light amount controlling unit of the conventional lens barrel 110 described above, when rotating the shutter lever 115 for driving the shutter blades as shown in FIG. 19, the shutter lever 115 is pressed by the head of the plunger 105 of the electromagnetic unit 100 in the direction of the axis of the plunger shaft. The electromagnetic unit 100 is disposed in such a manner that the plunger shaft lies perpendicularly to the optical axis O of the lens along the circumference of the lens frame.
Therefore, a large space, for example, a space of Do in diameter, is required for disposing the electromagnetic unit 100 in the lens frame 111, which results in increase in useless space, and stands in the way of downsizing the lens barrel.
The disposition of the electromagnetic unit with respect to the lens frame in the light exposure controlling unit disclosed in Japanese Unexamined Patent Application Publication No. 4-194912 is almost the same as that of the electromagnetic unit of the conventional light amount controlling unit shown in FIG. 19, and thus has the same disadvantage.